1. Technical Field
The present disclosure relates to a process for manufacturing a membrane made of semiconductor material that is integrated in, and electrically insulated from, a substrate.
2. Description of the Related Art
A large number of integrated semiconductor sensors are known, made with micromachining techniques, which base their operation on detection of a deformation of a thin membrane (also defined as diaphragm), suspended above a cavity. Among these sensors it is possible, for example, to mention absolute or differential, capacitive or piezoresistive, pressure sensors, inertial sensors, chemical sensors, magnetic-field sensors, and microphones. It is also known that it is often advantageous, or even necessary, to provide an electrical, and possibly thermal, insulation of the membrane.
Main known techniques for manufacturing electrically insulated membranes envisage the use of a SOI (Silicon On Insulator) wafer, or of surface micromachining techniques, with selective removal of sacrificial layers (e.g., a field-oxide or buried-oxide layer). According to these techniques, a substrate of semiconductor material is used only as a mechanical support.
The aforesaid techniques are in general complex to implement and involve considerable manufacturing costs.
European patent application No. EP-A-1 577 656, filed in the name of the present applicant, discloses a process for the manufacturing of a membrane of monocrystalline silicon suspended above a cavity, buried and entirely contained within a substrate, which is also made of silicon. This process is extremely simple and economically advantageous, and compatible with the integrated manufacturing of corresponding electronic circuits; also, the resulting structure has small dimensions.
However, the problem of electrical or thermal insulation of the membrane thus obtained has not yet been adequately solved, so that this manufacturing process is not currently completely exploitable in applications in which the insulation of the membrane from the substrate from which it is obtained is required. In particular, it is advisable to prevent structures for electrical insulation of said membrane from altering the mechanical behavior thereof, in particular the capacity of deformation due to external stresses, and from causing in general reliability problems.